Marshall MG250DFX

[casey73]

I'm a tube amp guy and have little experience with solid state amp repair. But I have built many effects pedals. My neighbor asked if I could take a look at a broken phaser pedal for his friend. I agreed and they came by yesterday. The guy did an "oh by the way" could you look at my Marshall MG250DFX as long as I have it here. I told him I wasn't really a solid state amp guy but as a favor I'd look at it.

The guy said he wants to give it to a young nephew but when he turned it on, it sounded great but he could smell smoke and shut it down. I haven't powered it up yet. My quick research says this particular amp has a history of unreliability particularly in the power amp section. I'm thinking anything that causes smoke is likely coming from the power supply/power amp. I'll open it up to see if there are obvious signs of heat damage, but I don't want to spend alot of time on it if it's a lost cause (i.e. not worth repairing).

Anyone here familiar with this amp? It is even worth repairing? Based on what I've read, even when the amp works it's not real desirable in terms of tone.

[Enzo]

There are way more of them that work than there are that burnt up.  What you see on the internet is not a fair representation of a product.  No one goes on a repair forum to say "Hi, I just joined, I have no problems with my amp."

But WHEN they fail, by far the most likely part is one of the power amp modules.  Look close, see any blackening under the IC where the legs come out?

Usually a new power module and it is OK.

[casey73]

Thanks for your input Enzo. I had a feeling I might run into you here. 'No one goes on a repair forum to say "Hi, I just joined, I have no problems with my amp."' That's kinda funny, and also true in this case.

I agree it isn't fair to judge a product based on internet talk because most people don't say anything if they are happy with a product but will leave a review if something goes bad for them. The only bad review I ever left was after I got take out Kung Pao Chicken from a very marginal Thai restaurant, when I could find almost no chicken among the sea of onions.

As for the amp, I found power chip replacement modules for about $40. I'll open it up tonight and see what's going on. I don't think the guy wants to sink much into it.  I may barter for a 12 pack of beer and a couple rolls of toilet paper plus parts.

[joecool85]

At a bare minimum you've got a snazzy looking 2x12 combo chassis with speakers!  Very worse case, gut it and put in new electronics.   :tu:

[casey73]

Opened it up and it's clean inside, all original. No sign of any heat damage anywhere. Power modules are bright green and look great. Plugged it in open chassis and cranked it for a while to get the heat sinks warmed up. All looked normal and sounded normal. No smoke other weird smells.

[Enzo]

Well, that is an important part of any repair - making sure the problem exists.   People are easily fooled.

You can buy the whole module - and be aware there are a couple types that are similar but not compatible.  These had the 15 pin connector.  But on some other models have an 8-pin connector plus a 3-pin one.  Same IC on them, but wires difffer.

Either way, usually the little module itself is OK, just the TDA7293 power IC on it is dead.  So I just replace the IC and reuse the module.